<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>变量和数据类型</title>
</head>
<script type="text/javascript">
    //单行注释：声明变量并使用；typeof判断数据类型
    var number1 = 10;
    document.write("number1的数据类型是："+typeof number1);
    var b;
    document.write("<br/>b的数据类型是："+typeof b);
    var c = undefined;
    document.write("<br/>c的数据类型是："+typeof c);
    /*
        boolean
        表达式
     */
    var result = 5>3;
    document.write("<br/>result是："+result);
    document.write("<br/>result的数据类型是："+typeof result);

    var str = "hello";
    document.write("<br/>str："+typeof str);

    var str2 = null;
    document.write("<br/>str2："+typeof str2);

</script>
<body>

</body>
</html>